ee PHYSICS. 
In Germany, and other countries nearly of the same latitude, snow gene- 
rally falls in a quiet atmosphere; sometimes, however, and particularly in 
February, the falling of snow is accompanied by tempestuous weather. The 
wind in such cases frequently passes during the storm from west or south- 
west to north, and after the fall, cold weather with a clear sky sets in. On 
high mountains, and in mountainous regions, the falling of snow is often 
accompanied by winds which are not far behind the most violent storms in 
intensity, hence they are called snow storms. The snow storms of the Alps, 
so dangerous to travellers, are well known to all. At higher latitudes these 
storms occur at a less elevation, particularly in Norway and Kamtschatka, 
where they are called Purga. That such snow storms ought to be ranked 
with thunder storms is shown by the electrical condition of the atmosphere, 
and by the lightning which not rarely accompanies them. 
The quantity of snow deposited differs with the year and country, being 
very variable for slight elevations above the level of the sea. More snow 
falls in valleys and woody districts than in the level land. The snow 
increases from the isothermal of 59°F. in the north, to the isothermal of 
41°F. which passes by Drontheim; it then diminishes, since in the 
high northern latitudes the air is too cold to contain much moisture. 
The quantity of water which may be obtained by melting snow differs 
greatly at times. During severe cold and northern or north-eastern winds, 
the snow is very loose and balls together with great difficulty, indicating the 
existence of little water. In general, the snow is lighter the more there is 
to be of it; hence the proverb, “much snow little water, little snow much 
water,” is well founded. According to De La Hire, water is 3}—12 times 
denser than snow; according to Celsius, 24—11 times; according to Van 
Swinden, 54—19; according to the more recent investigations of Quetelet, 
24-18 times. In general, the density of snow may be assumed at $—,\. 
Freshly fallen snow is always the lightest. gradually becoming firmer by its 
own pressure, and finally acquiring an icy crust by the melting of the super- 
ficial layers and subsequent freezing of the water. A considerable and quite 
appreciable diminution in the amount of snow on a given surface may be 
observed after it has lain a good while in a dry atmosphere. It is well 
known that snow, by its badly conducting power, acts as a preventive to 
the direful influences of the freezing of the ground. 
Snow water is generally pure, being only exceptionally mixed with 
foreign ingredients, for which reason it is of no especial use to vegetation, 
being rather prejudicial on account of the coldness. The beautiful red 
color of snow first observed by Saussure (1760) in the Alps, owes its redness 
to minute alge (Protococcus nivalis). Green snow is caused by Protococcus 
viridis. 
Of Hail. 
Hail, one of the most peculiar phenomena in meteorology, is divisible 
into two principal classes: Ist. Sleet, composed of round granules, generally 
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